The field of the invention is cutting or shredding of a collection which collection is compressible. The term "compressible" is meant to refer to an aggregation of pieces of material which aggregation is compressible to an essentially void free state. The process of the present invention is particularly effective for comminuting a collection of elastic compressible materials such as pieces of vulcanized rubber. It is also useful for comminuting a collection of less elastic materials such as used carpets which can be compressed from an original low density configuration to a compressed high density and essentially void free material when subjected to sufficient pressure.
Perhaps the most common problem is that of pulverizing vulcanized rubber. The amount of waste created by discarded tires has created a worldwide waste removal problem which to date has not been solved in any practical manner. Another less known waste problem is the discarded sprews which are created when rubber parts are transfer molded. Unlike plastic waste which can be reprocessed by melting, cross linked rubber is not meltable and, thus, not easily re-processed. Various chemical methods are known which digest and permit such cured rubber to be reclaimed, but the reclaimed rubber degrades the quality of the final molded parts so that it can be used only in low grade applications such as floor mats. Various mechanical rubber grinders have been developed. Intermeshed wheels have been used, such as that shown in U.S. Pat. Nos. 4,052,013 and 5,048,764, but such devices of this type are limited in the particle size which they produce. For instance, in the tire shredding apparatus shown in U.S. Pat. No. 4,052,013, the ground rubber particles merely have to pass through a screening drum with openings of 3" diameter to produce a particle which is suitable as boiler feed. Unfortunately, the burning of rubber particles requires the need for expensive air pollution removing means since the rubber contains sulfur and other products which are capable of creating highly toxic products of combustion.
U.S. Pat. No. 5,100,069 utilizing interlocking shearing blades produces particles having a size less then 1" by 1". If the rubber particles are sufficiently cool they cease to be compressible and may be crushed in equipment of the type utilized for crushing rock and other solids. Such a process is shown in U.S. Pat. No. 4,813,614.
A machine which claims to produce a very finely powdered rubber is shown in U.S. Pat. No. 984,758 where particles of rubber are pushed against a wheel which has a grinding surface. Such a process generates a great deal of heat and for that reason, air is forced through the particles of rubber before they hit the grinder and air is also forced through the grinder to try to cool the face of the grinder.
A cutter wheel is shown in U.S. Pat. No. 5,375,775 which reduces vehicle tires to very fine particles by passing tire treads against a wheel with extending knives which form a shearing action against a fixed blade assembly 26.
Uncured rubber is not cross linked and may be readily softened and extruded in spaghetti-like rods and cut by moving blades as shown in U.S. Pat. No. 2,215,435. The resulting product is compared to corn flakes which are dusted with carbon black to prevent them from sticking together. Such flaked crude rubber is more easily processed than the unflaked bales of crude rubber.
Another machine for cutting up crude rubber is shown in U.S. Pat. No. 3,001,728. This process operates on uncured rubber, not a cross-linked product. Russian Patent No. 982,797 shows another device which cuts up bales of rubber which are uncured.
German Patent No. 1,298,867 shows a device for disintegrating plastic waste material which utilizes a cutter which is fed by a piston. Japanese Patent No. 5-329,389 grinds waste rubber by rotating an abrasive cone in a conical chamber which is fed by a screw. The process creates a great deal of friction which heats the rubber and thereby vaporizes the sulfur, which of course, creates air pollution and waste disposal problems. East German Patent No. 212,694 reprocesses rubberized cord fabric. A ram covers the length of the hopper but only half of the width of the hopper. A screw forces the material through a hardened nozzle over which is located a rotating cutter which rotates coaxially with the screw and has a number of blades which cut the rubberized cord into smaller pieces.
Japanese Patent No. 3-60748 utilizes a screw which pressurizes rubber pieces and extrudes them through a plate containing holes. The projected pieces are cut by a cutter fitted at the end of the screw shaft. This design is not unlike a conventional meat grinder.
A Russian Patent No. 1351-666 shows a device for milling clay with hard lumps. The clay is fed by a screw into a compacting head which feeds the lumpy clay against a rotating cutter. Such lumps of clay would be considered friable or easily breakable conglomerates unlike pieces of cured rubber.
To summarize, there are many machines capable of breaking vulcanized rubber particles into small pieces such as 1" diameter chunks. Processes which are capable of further breaking down compressible cross link materials into a very fine powder in the past have generated a great deal of heat which creates toxic or noxious fumes, which, in today's industrial setting, would be unacceptable. There is, thus, a need for a process which is capable of turning such materials into a very fine powder which does not generate significant heat, and yet, reduces the end product to a very fine powder, such as 100 mesh or 200 mesh. When cured rubber is broken down to this fine consistency, it can be added back to finished product and actually have no deleterious effect on the virgin rubber at all. Thus, a waste disposal problem is converted to a valuable raw material.